A letter mailed to a mississippi senator has tested positive for the deadly poison ricin and the senate suspended mail delivery as investigators try to determine who sent it and why. Abc's senior justice correspondent pierre thomas joins us with more. This echoes the anthrax scare in the capitol after 9/11. Reporter: It does. The senate is on high alert and all mail to the capitol has been stopped while the fbi awaits test results to see if the letter sent to roger wicker was lace the with the deadly poison ricin which can be fatal if inhaled or ingested. It was postmarked in memphis, tennessee and intercepted in landover, maryland, after two field tests showed a positive hit for ricin. Sources are telling us those field tests are notoriously le and a more definitive test being done at a laboratory. We should know those results in the next 24 to 48 hours. But investigators already do believe, pierre, and told senators that there's no connection, they believe, to the boston bombings. Reporter: Yeah, no connection to the boston bombing and I can tell you, george, there is a person of interest who is known for sending angry letters to capitol hill. That person will be receiving a knock on the door.

This transcript has been automatically generated and may not be 100% accurate.

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